X-ray apparatus

ABSTRACT

599,726. X-ray tubes. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 18, 1943, No. 17065. Convention date, Oct. 22, 1942. [Class 39 (i)] [Also in Group XX] X-ray apparatus comprises a sealed casing forming a compartment containing an X-ray tube resiliently supported therein and electrically insulated therefrom by means comprising synthetic rubber material and surrounded by a gaseous insulating medium, such as a halogen derivative of an aliphatic hydrocarbon, adapted to be delivered into or displaced from the compartment through means located in either or both of two end coverplates attached to the casing, storage means for the gaseous insulating medium being attached to one end cover-plate and connected with and thermally insulated from the compartment to maintain a constant pressure therein. As shown in Fig. 2, the housing 11 contains an X-ray tube 13 comprising a rotating anode 15 and a cathode 17 mounted within a sealed envelope 19. An anode connection 21 and filament conductors 25 are provided. The anode may be rotated by the motor 27. The housing 11 has an opening 33 provided with an annular collar 35 forming an outwardly extending hood, and is closed by a cup-shaped plate 37. The housing 11 I is provided on the opposite side with chambers 43, 44 closed at one end and open at the other to receive cable terminals. The ends of the housing 11 are closed by plates 59, 60. The bracket 65 attached to lug 63 of the housing 11 has a circular aperture receiving a resilient neoprene disc, to which is secured by a bolt a moulded insulating bracket 85 carrying the anode connection 21. The cathode end of the tube is supported by a metal bracket 95 carrying a resilient neoprene disc having a central opening receiving the end of the cathode stem 29. A central opening in the cover-plate 59 is closed by a threaded plug 115, and a central opening in the cover-plate 60 is closed by a threaded fitting 119 having an opening containing a valve comprising a spring-pressed ball and closed by a threaded plug. The housing 11 may be charged with dichlorodifluoromethane or dichlorotetrafluoroethane through the valve in fitting 119, the plug 115 being removed to allow escape of displaced air. Alternatively, the air may be exhausted from the casing by connection of an exhaust pump to a threaded port 141 communicating through the duct 139 with the opening 137 adapted to be closed by the plug 115. The fitting 119 may be kept closed or replaced by a solid plug and the exhausting and charging effected entirely through the duct 139. An auxiliary casing 143, Fig. 6, may be provided with a pipe 145 adapted to be secured in the boss 113 of the cover-plate 60, the other end of the pipe 145 extending within casing 143 to form a liquid trap preventing passage of liquid to the casing 11. The casing 143 is fitted with a charging opening 147 closable by a plug 149 carrying a valve member 151 controlling gas flow through the pipe 145. The pipe 145 is of non-conducting material to thermally insulate the casing 143 from the casing 11. Specifications 555,013, [Group XX], and 557,631 are referred to.

Oct. 23, 1945. z J, ATLEE ETAL Y 2,387,427

X-RAY APPARATUS Filed oct. A22, 1942 Patented Oct. 23, 1945 X-RAY APPARATUS Zed .L Atlee,v Elmhurst, and `James C. Filmer, Wheaton,Ill., assignors to General Electric X-Ray Corporation, Chicago, Ill., a. corporation of N ew` York n Application october 22, 1942, serial No. 462354 (ci. 25o-90) 14 Claims.

`I'he'present invention relates in general to electrical-insulation and has more particular reference to means for and method of insulating X-ray generators in shockproof manner, the invention relating to the use of an evaporable `liquid mediumin the shockproof housing of an X-ray generator or tube for insulating purposes, includingjnovel features of tube housing design for the accommodation and utilization of the evaporable medium in gaseous condition for insulating pur- An important object of the invention resides in Using, as` an insulating medium for electrical equipment, a medium which normally exists in its liquidphase at low temperature or when under compression,` butfwhich vaporiaes` at a relatively `lowiemperature at atmospheric pressure; a further `object being to employ a chlorine-ilumine derivative of aliphatic hydrocarbons for insulating electrical apparatus, especially X-ray generators.

Another important `object is to utilize a chlorine-iluorine derivative of methane or ethane, which have a substantially gaseous phase Within thefrangeof temperature normally encountered within the range of` electrical devices; a further objectbeng to. emp1oy dichloro-difluoromethane,

CCI".2F2, or dichloro-tetrauoroethane, CzCl.zF4, preferably the latter, as an insulating medium.

` `Another important object is to provide an iinproved shockproof mounting for an X-ray generator comprising a casing; in which the generator may be supported, and means for charging the insulating medium in the casing after the same has been closed and sealed upon the generator.

Another important` object is to provide a substantially sound and shockproof casing for an X-ray generator, more particularly a generator of the rotating anode type, the operati-on of which develops a certain amount of undesirable noise andvibration; a further object being to eliminate andhvibration by supporting the Vibrator in its shockproof housing by means of resilient sup. ports embodying tube mounting elements of rubber-likefmaterial, while insulating the generator by ai gaseous atmosphere comprising an evaporablewmecliumy capable of maintaining a desiredpressure `within `the housing by evaporation therein from the liquid phase at the operating temperature of thegenerator; a further object being to. utilize an insulating medium inthe pres-k ence of which the rubber-like mounting elements do not appreciably deteriorate.

` ]Afnother important Objectis to employ an in sulating medium for the purposes mentioned, the

gio

medium being progressively evaporable with increase in temperature toproduce a corresponding increase in pressure within the generator housing, the medium 4having the further characteristic of 1 increasing-its dielectric strength in proportion to increase in pressure `Another important'` object is to provide an improved shockproof X-ray generator housing of minimum Weight and compactness, which through Y the employment ofv an evaporable insulating medium therein is characterized by the `absence of' reservoir and other attachments heretofore necessary in apparatus of' the character mentioned for maintaining a supply of liquid insulating me dium in the housing.`

- lating medium in place of the liquid` oil heretofore usedls and incidentally to-facilitate the operation and servicing of Xr`ay apparatus, since the weigh-t, in liquid condition, of the evaporable medium employed for insulating any-selected generator in accordance with the teachings of the present invention, is approximately two per cent of thel weight of' oil' required for insulating `a generator of' like size in accordance with previous insulating technique.

These and numerous other importantv objects, advantages, and inherent functions of the invention will be fully understood from the following description, which, taken in connection 'with the accompanying drawing, discloses a preferred embodiment of the invention.

Referring to the drawing Figure 1 is a perspective view of a generator housing embodying the present invention;

Fi'gureZ is a sectional View taken substantially along the line 2"-2 in Figure 1, showing the X-ray generator in mounted position Within the housms: Y v v Figure 3f is an enlarged sectional View taken througlfi` the generator mounting shown in the' right-hand end' of the generator, `as illustrated in Figure 2;

`Figure 4 is an Aenlargedsectional" view taken through the generator mounting shown at the left-hand end of the generator', as illustrated in Figure 2; y

i Figure 5 is anV enlarged sectionalv view taken substantially along the line 5`5 in Figure 2; and

Figure 6 isa sectional view showing a housing attachment comprising a reservoir. To illustrate the invention the drawing .shows a housing II for an X-ray generator I3, which,`

the filament is electrically energized, electrical` power for energizing the filament vbeing delivered thereto by filament conductors 25 extending outwardly of the envelope through suitable conductor seals. t

The X-ray generator I3 may comprise a generator of the sort illustrated and described in :the co-pending application of Zed J. Atlee for United States Letters Patent for X-ray tube, Serial vNo.'39(),322, filed. Apri1'25, 1941, upon which Letters Patent No. 2,311,725 issued February VV23', 1943, inwh'ich the anode I5 is caused to rotate within the envelope by motor means 21 disposed outwardly of the enveloperportions I9 enclosing the anode, the motor being mounted on a suitable bracket 28 in the casing in position to receive the anode end of the generator. The cathode I1 carries a stem'29 extending axially outwardly of the envelope at the cathode carrying end thereof, said stern being preferably fitted with an insulated terminal block 3| to which the lament conductors 25 are connected.

. The housing I I is generally cylindrical and provides a generally cylindrical cavity 30 for receiving the generator I3. The housing II 'is provided with an opening 33 and the housing is provided with an annularrrim or collar 35 forming anioutwardly extending lhood at said opening. The opening 33 is covered and closed by means of a plate of preferably cup-shaped configuration and having a marginal flange 39 sealingly secured, as

by screws 4I, on anannular seatV 42 formed in the hood 35. y

The housing `I I, preferably at its` side opposite from the opening v35, is formed'with a pair of spaced apart chambers 43, 44, the walls of which are formed integral with the walls of the housing.v 'These chambers 43, 44 are each closed at one end, asM shown at v45, and are open at the other end to receive cable terminals 41, 48, which may be `inserted axially within the chambers 43, 44 whereby to electrically connect cables' 49, 58 with terminal blocks 5 I and 52, respectively, supported within the closed ends of the chambers 43, 44 on terminal receiving sleeves`53, 54, of tapered cylindrical configuration, which receive the cable terminals 41, 48 within the chambers 43, 44. These receptacles are flanged, as at 55, at the open ends thereof for sealing connection with corresponding annular flanges at the open ends of the chambers 43,44. The inner, or closed, ends of the receptacles are tted with the terminal members 5|, 52 through whichthe conductors of the cables 49, 59 may be electrically connected with conductors within the housing II when the terminal members 41, 48 are inserted in said receptacles 53, 54. i

At each of itsopposed ends the generally cylindrical housing is preferably formed with cover flanges 51 affordingseats for receiving the peripheral edges jo`f preferably disc-like cover plates 59, 60, which are'sealingly secured upon the open ends of the housing, as by means of fastening screws B I.

Near one end of the housing II the same is provided internally with a bracket support lug 83 on which a bracket 65 is fastened, as by means of a clamping screw 61. The bracket 65 is provided with`an ear 69 having a circular opening .1 I. i Within the opening the ear is formed to pro- Vide an vannular seat 13 adapted to snugly receive the rim 11 of a resilient mounting member. This mounting member comprises a disc or diaphragm 19 of resilient, preferably rubber-like material such as neoprene, a synthetic rubber compound. The disc 19 is snugly fitted within and secured to the rim member 11, which preferably comprises a metal ring Within and to which the peripheral portions of the diaphragm member 19 are adhered, as by applying heat and pressure. The disc 19 is formed with a central opening within which is mounted a preferably metal sleeve 8| forming 'ahub in which may be mounted a stem 83, preferably in the form of a threadedscrew. This screw serves yto secure a bracket on the hub 8|. The bracket 85 preferably comprises molded insulating material, such as Bakelite, and has a portion extending at the longitudinal axis of the casing I I near an end thereof, said bracket portion being formed with an opening, for receiving the projecting end of the anode stem 2 I. i,

The bracket 85may conveniently comprise a machine finished die casting of aluminum or other suitable material, and the peripheral edge of the resilient mounting memberl 19 may besecured in the seat 13 by means of a removable retaining ring 81. The bracket 65, with attached mounting 19 and the insulating bracket 8 5, mayy be assembled in the casing II through the open end thereof, and the bracket 85 may alsoform a mounting for aiding in the ksupport of the motive means l2-1. The support bracket means 63, 85 and the motive means 21 having been assembled in the casingrthrough one end thereof, the generator I3 may thenbe mounted by inserting the same through the opposite open end of the casing, the anode carrying end being advanced in the casing through the motive means 21 until the stem 2| is received-in the opening formed therefor in the bracket 85. lThe stem 2| may be secured on the bracket by means ofnja fastening screw 89. The bracket '85 carries a 'terminal thereon connected with a conductor 9|, said terminalV being adapted to make electrical Vcon-v tact wth'the stem 2| when the same is'Y in mounted position on the-.bracket 85., The conductor 9| is connected with one of the terminals 5| of the cableireceptacle whereby the anode of the generator. I3, when the same is mountedfon the bracket 85,*may be electrically connected-with one of the conductors of one of they cables 49. Conductors 93 for energizing the'motive means -21 may be connected with others `of theV terminals 5I whereby to energize the motorthrough said cab1e49.

After the generator has thus v'been secured on Y the-bracket 85,- its cathode end may be anchored in position 'and electrically connected with the cable, 50 by means of a bracket 95,ipreferably comprisingv aV strip'of metal anchored -on a grounded bracket 91 which in turn is fastened on the inner, or closed, end'of the receptacle 53 in the" chamber 44. The strip 95 extends to the central axis of the casingv Aand1is formed with' anopening 99 which receives the projecting end' ofgthe, cathode'stem 29 the memberf95'-being assurer 99X The |f03pref'erably comprises rubberlike" material, such as neoprene, `a synthetic rubber,` `and is formed withv a. central opening" |01 snuglyreceivingthe stem 29 whereby the saine is resiiientlysupported on the member 95. The nlanicnt conductors 25 may then be electrically connected with the conductors of the cable 5U' by aannemen at the terminal plate si with conductors IUS extending to and `electrically connected with the terminals 52'. The cathode stein 29 may be grounded by means of a conductor I I I securedlto the end of the stem 29 and electrically connected with the grounded mounting member 95. b b b i Thefcasingll Ifmay beformed in any preferred fashion and may comprise an integral' casting. Preferably, however, and as` illustrated, the casing `|"I` comprises a sheet metal tube formed integlallyl With the chambers 43 41 the hOUd 35 preferably comprising aseparately formed mem berwelded or otherwise securedto the casing II atthefopening 33.` The flanges 5l at the opposite `ends `of the-casing and the flanges atY the open ends of; the chambers 43 and 44 may comprise strengthening rings welded or otherwise. attached tothe casing at the openings thereof.

l fTh'el cover plates 59 and 6U may be, formed in any suitable or convenient fashion and preferably comprise die` castings. Each cover member is.

formed With"a`centra1 embossment I|3 definingy an opening therethrough, which` opening. is normally closed by preferablythreaded means. To thisend the opening in the cover 59 may be closedby a threadedplugv I I5, while the opening in thecover 69 is closed preferably by vali/england means` ILI; thedetails of which are illustrated in Figure 5 of the drawing.

Thevalved gland meanslIII preferably cornprises "a threaded fitting IIS adapted to bev fastened in the opening to be` closed. The fitting |`|"9` `isfformecl with a longitudinal channeL |2| therethrough, which, channel forms `a valve seat |23 facing inwardly f of the fitting. Outwardly of." the valve seat the channel |2| is enlarged and internally threaded, as at |;25, inY order to receive. a threadedsealing plug .'I2`I. The `valve seat |23 adapted to seat a valve member |29-, prefer-l ably comprising a steel ball, which is ,normally uifgedtowarcl valve seating position by means of a"valveyspring|3| extending inthe channel |2| adjacent the ball. The spring |3| is retained in place preferablyby meansu of a plug |33 threaded inte` anenlarged portion of the channel |2I, said;

plug` |33 having a central perforation |35.

`The"generator I3 having been assembled in the; casing I andthe casing closed by theV covers;

59fand 6I! and by the assembly `of the. terminal receptacles 53 54 in the housings 43 and 44, .thel

housing may becharged with a suitable gaseousl insulating medium. For the purposes of the present invention, the gaseous insulatingr medium comprises a chlorine-luorine derivative of aliphaticlhydrocarbons, more particularly the halogenfderivatives of methane or ethane. Specifically the present invention teaches: the utilizationof dichloroTdifluoromethaneL CGLzE'z, or dichlnroftetrailuoroethane;CiCLzEi, and prefen.

Aperature, so that either dichloro-diiluoromethane or dichloro-tetrailuoroethane may be employed,

since both have vapor pressure characteristics such that they exist substantially in the vapor stage even under appreciable pressure at the normal operating temperature of X-ray generators, the boiling point of dichloro-difluoromethane being minus twenty-eight degrees centigrade, while the boiling point of dichloro-tetrafluoroethane is albout four degrees centigrade at atmospheric pressure. l

Both of these media, in gaseous condition, have dielectric strength appreciably greater thanthat, of dry air and have insulating characteristics rendering them particularly well suited for insulating X-ray generators in shockproof casings, since neither of them have any material effect upon the rubber-like mountings 'I9 and |03 and both` are non-toxic. I

The insulating medium may be charged into the casing through the iltting ||9 by removing the plug |21 and attaching a conduit leading. to a supply source, which may be a receptacle containing the medium in liquid condition. By heating the liquid to vaporize the same, the same may be charged into the casing through the check valve |29. During the charging operation the valve ||5 is opened to allow air to escape from the casing, the valve being closed when the air has been displaced. Satisfactory results are obtained'by merely flushing" theV air fromthe casing by introducing the gaseous insulating medium through the inlet fitting and allowing it to flush out the air, since the presence of a small amount of air in the casing with the insulating gas does not: materially impair the insulating effect.

It is preferable, however, to provide for exhausting the air from the chamber, and this may be accomplished by forming the cover pl'ate 59v with'a duct |39 opening into thecasing through a valve seat. |31, the duct openingV outwardly ofv the, plate at a preferably threaded port|4 adapt'- ed for connection with an exhaust pump. After air has been exhausted from the casing, the plug may be set upon the seat |37 to seal the duct |39 and the insulating gas allowed to enter through the fitting ||9 under control of a valvein the conduit between the supply receptacleand the fitting, such valve being kept closed while the `chamber is: being exhausted of air. v

As: an alternative method of charging the cas-` ing, the tting I I9 may be kept closed or replaced by a solid plug, and the exhausting and charging of the casing accomplished entirely through the duct |39. This may be accomplished by connecting the supply reservoir in the exhaust l-ineV to the duct |39. By closing the connection to the reservoir and opening the connection to the pump, the casing may be exhausted of air through the duct. |39. Then by closing the connection to the. pump and opening the connection to the res'-4 ervoir, the exhausted casing may be filled insulating gas thro-ugh the duct. When sufficiently charged with gas, the plug; |I5 may bef turnedto. seal the duct` |39v at the valve seatI'3`I` It is desirable to make the casing light in weight and, consequently, the walls thereof are made as thin as possible, with due consideration for requisite strength. The thickness of the casing walls and consequent strength thereof imposes a limitation on the maximum internal pressure to which the casing may safely be subjected. If the casing be sealed as above described and subjected to high temperatures due to the release therein of heat by the operation of the X-ray generator, the gaseous pressure may increase to dangerously high levels if the casing be of light weight, relatively weak construction. The gas pressure in the casing, however, may be kept at its pressure corresponding with room temperature by connecting it with a chamber or zone, which is thermally isolated from and in open communication-with the casing. f By holding the temperature of the chamber at room temperature, the gaseous medium will ow into and condense in the chamber on any pressure rise in the casing, thus maintaining the pressure at the room temperature pressure of the medium and insuring against the development of excessive pressures in the casing.

To that end, an auxiliary casing |43, forming a supply reservoir, may be provided and itted with a delivery pipe |45 having an end projecting from the bottom of the casing |43 in position to be secured in the boss ||3 of the cover plate 60, in open communication with the interior of the casing I. The other end of the pipe |45 extends substantially within the casing |43, thereby forming a liquid trap preventing passage of liquid from the casing |43 to the casing through the pipe |45, no matter how the casings may be tilted. The pipe, however, allows free gas passage between the casings.

The casing is formed with a lter opening |41 in its top wall, preferably opposite the inner end of the pipe |45. This opening allows liquid to be charged into the casing |43. The opening is normally closed by a removable plug |49, in which may be fitted a valve member |5| operable outwardly of the plug to control gas flow through the pipe |45. To this end the valve member 5| has an inner end adapted to cooperate with a valve seat |53, at the inner end of the pipe |45, to control gals flow while the casing is being initially evacuated. The valve member |5|, normally will be in open position and will be closed only when it is desired to isolate the casing |43 from the casing The casing |43 is preferably thermally insulated from the casing as by making the pipe |45 of vBakelite or other non-conducting material. The casing |43 consequently will be at a relatively lower temperature than the casing since all of the heat generated by the operation of the tube |3 is liberated within the casing As a consequence, any condensation of gas, during heating and cooling of the casing within the range of its maximum operating and stand-by temperature, will take place in the relatively cool storage casing |37 and not in the chamber At the same time, the liquid stored in the casing |43 provides a constantly available source of gas which automatically replenishes any gas lost byleakag-e.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacricing any of its attendant advantages, the form herein disclosed being a preferred embodiment for the purpose of illustrating the invention. The invention is hereby claimed as follows: `1. X-ray apparatus comprising a sealedcasing forming la compartment, an X-ray tube in said compartment, a gaseous insulating medium enveloping the tube in said casing, said medium having vapor pressure characteristics such that lit may exist, under pressure, in a liquid phase at normalatmospheric temperature, a storage chamber connected with said compartment and heat insulating means thermally. insulating said chamber from said compartment, the walls of said chamber being exposed to the surrounding atmosphere to maintain said chamber at a temperature su'iciently low to maintain an insulating medium, in liquid condition, therein.

2. X-ray apparatus comprising a sealed casing forming a compartment, an X-ray tube in vsaid compartment, a gaseous insulating medium enveloping the tube in said casing, said medium having vapor pressure characteristics such that it may exist, under pressure, in a liquid phase at normal atmospheric temperature, a storage chamber and insulated conduit means connecting said chamber with said compartment to thereby thermally insulate the chamber from the supply of insulating medium, in liquid condition,V

in the chamber.

3. X-ray apparatus .comprising a sealed casing forming va compartment, an X-ray tube in said compartment, a gaseous insulating medium enveloping the tube in said casing, said medium having vapor pressure characteristics such that it may exist, under pressure, in a liquid phase at normal atmospheric temperature, said casing having a storage `chamber connected with said compartment, means for cooling the walls of said storage chamber to allow a supply of the medium in liquid condition to be stored therein whereby an atmosphere of the medium in gaseous condition may be maintained in said compartment, and trap means normally preventing the medium from entering the compartment from the chamber when in liquid condition.

4. X-ray apparatus comprising a sealed 'casing forming a compartment, an X-ray tube in said compartment, and an insulating medium enveloping the tube in said casing, said tube being supported in the compartment on resilient support means comprising a disk of rubber-like material, a bracket el-ement carried by the casing, and a tube supporting element, one of said elements being secured to the said disk at the edge thereof and the other of said elements engaging the disk inwardly of its edge whereby to resiliently support the tube in the casing.

5. X-ray apparatus comprising a sealed casing supporting element, one of said elements beingy secured to said disk at the edge thereofjand the other of said elements engaging the disk inwardly of its edge whereby to resiliently support the tube in the casing.

6. X-ray apparatus comprising a casing having an open end and forming an elongated cavity for medium, abracket element carried by the casing and a tube supporting element, one of said elements being secured to said disk at the edge l thereof `and `the other of said elements engaging the `disk inwardly of its edge whereby to resil- `iently support the tube in the casing, and a hanger mountable in said casing after insertion of the tube in the casing and on the bracket, said hanger being mountable in position to receive and support the end of the tube remote from said bracket means.

'7. X-ray apparatus comprising a casing having an open end and forming an elongated cavity for an X-ray tube,`bracket means in said cavity in `position to receive and support one end of an X-ray tube when the same is inserted into the cavity from the open end of the casing, a hanger `mountable in said casing after insertion of the tube in the casing and on the bracket, said hanger `being mountable in position to receive and sup- `port the end of the tube remote from said bracket necting the tube with electrical operating circuits disposed outwardly of the casing, a removable cover in spaced relation with said supporting means for sealing the open end of said casing, and inlet means on said cover for delivering a gaseous insulating medium into the cavity from a source outside f said casing.

9. X-ray apparatus comprising a casing having an open end and forming an elongated cavity for receiving an X-ray tube, means for supporting the tube in the cavity and for electrically connecting the tube with electrical operating circuits disposed outwardly of the casing, a removable cover for sealing the open end of said casing, and inlet means on said cover for delivering a gaseous insulating medium into the cavity from a source outside of said casing, said inlet means comprising/means on the cover forming a duct therethrough, the duct being formed with a valve seat facing into the cavity, a spring pressed valve on the seat and a seal plug removably secured in the duct outwardly of the valve seat.

10. X-ray apparatus comprising a casing having an open end and forming an elongated cavity f`or receiving an X-ray tube, means for supporting the tube in the cavity and for electrically connecting the tube with electrical operating circuits disposed outwardly of thev casing, a removable cover for sealing the open end of said casing, said cover being formed with a duct therethrough communicating with said cavity, the duct being formed with a valve seat facing into the cavity, and a spring pressed valve on the seat past which a gaseous insulating medium may be delivered through said duct and into the cavity from a source outside of said casing.

11. X-ray apparatus comprising a casing having an open end and forming an elongated cavity for receiving an X-ray tube, means for supporting the tube in the cavity and for electrically connecting the tube with electrical operating circuits disposed outwardly of the casing, a removable cover for sealing the open end of said casing, said cover being formed with a duct therethrough communicating with said cavity, the duct being formed with a valve seat facing into the cavity, a spring pressed valve on the seat past which a gaseous insulating medium may be delivered through said duct and into the cavity from a source outside of said-casing, and a valved vent in said casing remote from the open end thereof to allow displacement of air from the cavity in filling the same with said insulating medium through said duct;

12. X-ray apparatus comprising a casing having an open end and forming an elongated lcavity for receiving an X-ray tube, means` for supporting the tube in the cavity and for electrically connecting the tube with electrical operating circuits disposed outwardly of the casing, a removable cover for sealing the open end of said casing, and inlet means on said cover for delivering a gaseous insulating medium into the cavity from a source outside of said casing, said inlet means comprising a storage chamber for the insulating material in liquid condition, the storage chamber being in open communication with said cavity through a duct extending in said cover and a liquid trap normally preventing entrance of liquid through said duct from the chamber to the cavity.

13. X-ray apparatus comprising a casing havring an open end'and forming an elongated cavity for receiving an X-ray tube, means forI supporting the tube in the cavity and for electrically connecting the tube with electrical operating circuits disposed outwardly of the casing, inlet means on said casing for delivering a gaseous insulating medium into the cavity from a source outside of said casing, and a valved vent in said casing remote from said inlet means to allow displacement of air from the cavity in filling the same with gas through said said inlet.

14. X-ray apparatus comprising a casing having an open end and forming an elongated cavity for receiving an X-ray tube, means for supporting the tube in the cavity and for electrically connecting the tube with electrical operating circuits disposed outwardly of the casing, inlet means on said casing for delivering a gaseous insulating medium into the cavity from a source outside of said casing, and a valved vent in said casing remote from said inlet means to allow displacement of air from the cavity in iilling the same with gas through said inlet, said valved vent comprising means forming a venting channel in the walls of the casing and a valve member ,operable outwardly of the casing for sealing said channel.

ZED,J. ATLEE. JAMES C. FILMER. 

